An aircraft is equipped with a large number of sensors making it possible to measure its flight parameters (speed, attitude, position, altitude, etc.), and more generally its state at each instant.
These flight parameters are then used by avionics systems, notably the automatic pilot system, the flight computers (Flight Control Computer Systems), the aircraft control and guidance system (Flight Guidance System), systems that are among the most critical of the aircraft.
Because of the critical nature of these systems, the sensors are redundant, i.e. a plurality of sensors supply measurements of one and the same parameter. These different measurements are then processed by a measurements merging method in order to provide the fairest possible estimation of the parameter. The estimation of the parameter is, for example, an average value, or a median value of a plurality of measurements each supplied by a distinct sensor. The estimation of the parameter is also called “consolidated value”, or “estimated value”.
In order to improve the estimation of the parameter, the measurements merging methods generally comprise a searching for a possible anomaly on one of the sensors, in order not to take into account an aberrant measurement supplied by a sensor exhibiting an anomaly.
For example, a measurements merging method is known that comprises, at each instant, the following steps:                calculation of the median value of the measurements supplied by the different sensors;        positioning of the measurements supplied by the sensors in relation to a tolerance band of predetermined width, centered on the median value;        elimination of the measurements situated outside of this tolerance band;        estimation of the value of the parameter from the remaining measurements.        
The step of positioning the measurements in relation to a tolerance band implements a searching for a possible anomaly on one of the sensors, this anomaly being revealed by the supply of an aberrant measurement.
One drawback with such a measurements merging method is that it does not make it possible to reliably determine a probability of false alarm, that is to say the probability of considering that a sensor is exhibiting an anomaly, although it is not exhibiting any such anomaly.